NEW YORK (CNN) -- Accused investment swindler Bernard L. Madoff will plead guilty later this week to 11 counts that could bring a sentence of 150 years in prison, one of his attorneys told CNN.

Bernard L. Madoff is charged in one of the largest investment fraud schemes on record.

Prosecutors stressed that there is no plea deal and that Madoff, 70, will have to forfeit any money he made from his crimes.

"The government has not entered into any agreement with Mr. Madoff about his plea or sentencing," said acting U.S. Attorney Lev L. Dassin. "The filing of these charges does not end the matter. Our investigation is continuing."

Madoff attorney Ira Lee Sorkin said his client has agreed to plead guilty to crimes including money laundering, perjury and fraud.

Earlier, Sorkin and defense attorney Daniel Horowitz told CNN that Madoff was waiving his right to a grand jury indictment and that the defense team had been talking about a plea with government attorneys.

Madoff is a former chairman of the NASDAQ stock market and founder of an innovative Wall Street trading firm that electronically matched buy and sell orders. He is accused of running a massive fraud, allegedly using new investment money from clients to fund other customers' apparent gains.

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"There is no innocent explanation," Madoff told two FBI agents, according to the complaint, which states Madoff expects to go to jail.

Madoff was charged in December with one count of securities fraud, which carries a maximum sentence of 20 years in prison. He has remained out on $10 million bail, but is confined to his luxurious Upper East Side apartment.

In court documents, prosecutors said Madoff had run his scheme "from at least the 1980s until his arrest on December 11, 2008, ... by soliciting billions of dollars of funds under false pretenses, failing to invest investors' funds as promised, and misappropriating and converting investors' funds to Madoff's own benefit."

The charges also say Madoff's company, Bernard L. Madoff Investment Securities (BLMIS), claimed that as of November 30, 2008, it held 4,800 client accounts worth about $64.8 billion.

"In fact, BLMIS held only a small fraction of that balance on behalf of its clients," the documents say.

Madoff is scheduled appear at a plea proceeding on Thursday before U.S. District Judge Denny Chin.

Chin also ruled Tuesday that Madoff can keep Sorkin on as his attorney after Madoff said he was satisfied the attorney was representing his interests despite potential conflicts of interest.

Sorkin told the government he invested $18,860 with Madoff in the early 1990s through a retirement account that had been set up with his former law firm and was later transferred to another brokerage firm in 1995. Also, Sorkin's late father held an account with Madoff, the proceeds of which were eventually distributed to trust accounts for Sorkin's two sons.

Sorkin also has represented a Florida accounting firm, Avellino & Bienes, which invested with Madoff.

Sorkin told CNN he has received death threats and anti-Semitic hate mail.

CNN sent an e-mail to one of the originating electronic address but received no reply.

"These people need to take Civics 101," Sorkin told CNN. "It is extremely disappointing that people who should know better have no understanding of the role defense lawyers play in preserving our system of justice."

The senders display a "lack of understanding of the constitution and bill of rights and how it applies to everyone," Sorkin added. "As for the remarks I can only have sympathy for these people who treat this representation as some religious quest."